Our research interests focus on the topographical mapping of sensory epithelia in sensory cortex and their plasticity. We are particularly interested in delineating the spatial extent of cortical activation (e.g., the spatial spread of all the responding neurons) to small (point) stimulation because it is fundamental to our understanding of cortical maps. Functional imaging methods are advantageous for characterizing the spatial extent because of their ability to provide quick, high spatial resolution assessment of activity from large cortical regions. However, one limitation of most of the functional imaging methods is that they rely on hemodynamic events that follow brain activation and therefore provide only an indirect means for assessing the spatial extent of the underlying neuronal evoked activation and thus imagers lack the means to assess the spread of neuronal activation using imaging. Because there is no direct way to verify the spatial extent of the underlying neuronal activation area in humans, imagers typically apply conservative thresholds for analysis that typically emphasize peak, or near peak activation areas. Such practice, however, may lead to a biased and possibly distorted view of cortical function because it may underestimate the real size of cortical activation. To address these issues, it is proposed to directly relate the spread of neuronal activation to the spread imaged by functional imaging of the same cortical area with the same stimulation. The point stimulation is either a whisker or a pure tone, and the spread of cortical activation is imaged by intrinsic signal optical imaging in the adult rat somatosensory and auditory cortex, respectively. Imaging results will be directly compared to post-imaging neuronal recording using electrode arrays within the imaged cortex. Imaging and neuronal results, in turn, will also be superimposed on the anatomical maps of the same areas to highlight cortical structure-function relationship related to the spread of activity. Because functional imaging methods can detect both suprathreshold (action potentials) and subthreshold (local field potentials), the spread of both types of neuronal activations will be recorded and compared with imaging results. Once the rules of mapping neuronal spread to imaging spread are quantified, it will enable unbiased, direct, imaging-based description of the entire somatosensory and auditory cortices using such rules.